Chicago recorded a low temperature of about minus 23 degrees Fahrenheit (minus 30 Celsius) - not a record, but close to it. Minneapolis recorded minus 27 F (minus 32 C).
But some of the lowest temperatures in a generation could still arrive in parts of the Midwest and Ohio Valley on Thursday, forecasters warned.
Frozen water mains and strained natural gas supplies left the US Midwest struggling on Thursday as a deadly Arctic air mass had tens of millions of Americans shivering for a second day. Rockford saw a record low temperature of minus 31 (minus 35 Celsius), on Thursday.
Animals also had a tough time in the cold weather, including one horse who got itself wedged between two branches of a tree trunk in the subzero temperature.
In Fargo, North Dakota, where the temperature dropped to minus 24F (minus 31C), Dan Hallock, an advertising executive, marveled that people were still working outside as he bought coffee. "Please come back fast, we need you".
More than 1,600 flights were cancelled in Chicago by mid-morning. The conditions that had to line up for that temperature to occur Thursday morning were a long shot, but not impossible.More news: A major United States policy change began with one migrant’s arrival in Mexico
At least 12 people have died due to the plummeting temperatures that have plunged the United States down to minus 40 degrees celsius this week.
Hundreds of warming centres were opened for vulnerable residents such as seniors, buses were employed as mobile warming spaces, and shelter capacities were increased for the homeless, including the approximately 16,000 living on the streets of Chicago.
He said places in MI and IL that were experiencing record or near-record cold this week were expected to be around 10C by Monday, approximately a 40C turnaround.
Calling the temperatures "dangerous", Hobart said United was bringing in extra workers and providing heated tents for employees. "And because it's so cold, there won't be much of a warm-up Wednesday".
Authorities warned that the extreme temperatures were life-threatening, as Illinois, Michigan, and Wisconsin implemented emergency measures.
In Michigan, homeless shelters in Lansing were becoming "overloaded", Mayor Andy Schor said.
At least four deaths were linked to the weather system Tuesday, including a man struck and killed by a snow plow in the Chicago area, a young couple whose SUV struck another on a snowy road in northern in and a Milwaukee man found frozen to death in a garage.More news: Barcelona 6 - 1 Sevilla - Match Report & Highlights
Another man, 55, froze to death in his Milwaukee garage after he collapsed shovelling snow.
A wind chill advisory is in effect right through to Thursday. "I can feel my skin tighten up".
In Minnesota and Upper Michigan, people battled temperatures as low as minus 25F (minus 31C), said Andrew Orrison, a weather service forecaster.
The wind blows snow over the subway tracks on January 30, 2019 in NY.
Parts of north and central Georgia are expecting about 2 inches of snow or more in the coming days, along with freezing rain and ice-slicked highways.
America's northern neighbor Canada was also contending with extreme cold, with frozen water pipes, snarled travel on a major waterway, and temperatures as low as -40F (-40C) on Wednesday.More news: Alibaba Runs It Back With Solid Q3 Results